


Sans the Science Skeleton

by foxsgloves



Category: Undertale (Video Game)
Genre: Dadsans, Established Soriel relationship stuff, F/M, Gen, Post-Pacifist Run, Sans the Science Guy!
Language: English
Status: Completed
Published: 2016-01-26
Updated: 2016-01-26
Packaged: 2018-05-16 00:34:00
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 6,195
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5806411
Author URL: https://archiveofourown.org/users/foxsgloves/pseuds/foxsgloves
Summary: <blockquote class="userstuff">
              <p>In which Sans is persuaded to do some science demonstrations for Toriel's fourth grade class.</p>
            </blockquote>





	Sans the Science Skeleton

**Author's Note:**

> Sometimes you just wanna write a one-shot about Sans doing science, Bill Nye style, so... I hope y'all enjoy!

It was a perfectly good date night when Toriel asked Sans to do science.

Well, the date part was over, but they’d settled onto Toriel’s bed so she could flip through her snail book while Sans leaned against her and thought about how the fur around her neck smelled of cinnamon and burnt sugar, so it was still perfectly good. But every five minutes or so he would be rudely awakened from half-sleep, his eyelids clicking open, as Toriel shifted and glanced towards the door at a thump or a bump or the clatter of crayons being thrown.

“Sans,” she said, “do you know anything about physics?”

He came way too close to answering “I have a doctorate” before he managed to trap the words behind his grinning teeth. What he knew about physics could fill a book. Did fill a book, once, co-written with Doc W-D himself. “Theory and Application of Hard Light: Light Hard With A Vengeance.” Doc let him pick the subtitle.

All copies of that book (winner of the third hundredth and thirteenth Underground Semi Prize for Innovation in the Sciences, presented by King Asgore himself) were erased from time and space. Tori will never read it. He has no proof it ever existed. He couldn’t even reproduce most of the theorems from memory. And it’s not like he hadn’t tried.

He can't exactly make her the most convincing argument, either, when all his memories of other times are warped like they’re seen through thick and curved glass. Trying not to forget goes about as well as trying to hold water in his cupped hands. His bony fingers make a great sieve.

She might believe him. She might not. Evidence in favor of: she’d done it before. Evidence against: she’d done it before.

Past experimentation ratios leaned more towards for than against, but the chances against were definitely non-zero, and anyway she wasn’t a soft voice through a locked door anymore but big and soft and solid, with warm crinkles around her eyes and a huge, braying giggle and fur that smelled of cinnamon and burnt sugar.

I’ll tell her when she asks, he had decided, as if he meant it in the least, as if he didn’t know himself well enough to see that he’d be taking the low road of denial and cowardice the minute she brought it up. As if he hadn’t already tried to fend off every hint about his past with a jab of a joke.

And she hadn’t asked, anyway.

Instead he said, “I, uh, know some stuff. Why do you ask?”

She sighed. “We’ve just started the monster science portion of the curriculum, and Frisk has been getting a little frustrated with the homework. I’ve spent some time with them, of course, but it doesn’t seem to have helped. If you could, would you mind…”

At that point, if he said no he’d be making it weird. “Sure, I guess. I’ll go teach the kid some cool science facts.”

“Thank you, dear,” she said, and nuzzled the top of his skull. He slunk out before she could see him flush.

The kid was sprawled, defeated, at the kitchen table, bracing their cheek on their hand as they scribbled a large, angry red spiral over their worksheet.

“How’s it hanging, short stack?” He swung another chair around and sat with his chin resting on the back. “Heard you were having some technical difficulties.”

 _PHYSICS HOMEWORK_ , Frisk wrote, tearing the paper a little in response.

“Well, let’s see, kiddo.” He flipped the textbook over. “Basic forces? This is no fun for a kid.”

 _Science is hard_ , signed Frisk, then puffed out their cheeks, blew a blustery sigh, and wrote in cramped letters, _I’m just too dumb for this stuff._

“Hey now. We both know that’s the opposite of true.” A damn long time ago, when he was a babybones with scraped kneecaps and a mud-stained hoodie, he’d thought the same thing. “Anybody can learn this kind of stuff if they have the right teacher.” Which he’d had. “Which is why your favorite uncle is here to show you how science can be—“ he winked—“ _Sans-sational_.”

 _GROAN_ , signed Frisk, the corners of their mouth tugging up.

He shuffled his chair over to the fridge and yanked out a can of pop from Toriel’s secret stash. “And all you gotta do… is drink this soda. It’s a very important job. _Can_ you handle it?”

 _Are you bribing me?_ they wrote with a wrinkle of their forehead.

“Well, if you don’t want it…” He dangled the can in front of their nose. “I guess I’ll go give it to Tori instead.”

They snatched the soda, popped the top and drained it in one long gulp. “That’s more like it. Now go ask your mom for some of her extra yarn. Tell her we’re gonna have a real _knit_ time.”

He started with the spinning can trick, always a fan favorite with the squirts. A helluva long time ago—in what he thought of as his first lifetime, when he always remembered which birthday it was Pap was egging him to celebrate and he always woke up where he’d gone to sleep, with limited and special exception—the can trick was the first thing W-D ever showed him, on the grassy slope outside New Home. Doc got his long, draping lab coat wet and covered in mud clods and grass clippings, and groaned about it all the way home.

The can cracked a real smile from the kid, and when they moved on to the density jar and Frisk watched the stripes of liquid meld and separate again and again, pressing their nose to the glass so they could watch up close, he’d even found some dimples. In between renditions of the little dance routine they invented to shake it up again they even managed to struggle through some actual math.

“Are you having fun, my child?” Toriel asked as she swept into the kitchen. Frisk bobbed their head up at her, raising the jar for another shake. “What did you and Sans make?”

Frisk gestured to the helpful label they’d written, _DENSITY!!!_ , and held up the jar for Toriel to survey. “How lovely,” she said. “But Sans, these experiments have absolutely nothing to do with our curriculum.”

“Frisk, show Mom your math,” he said with a lazy wink to Toriel. Frisk waved a pageful of finished equations in front of Toriel’s nose.

“Very nice work, my child. Why don’t you go get ready for bed? Perhaps Uncle Sans has time for the Mettaton show tonight.”

After Frisk scurried into their bedroom, she said, “That is quite something. I haven’t seen Frisk with this much enthusiasm for schoolwork in quite a while. How did you manage it?”

He shrugged, lacing his fingers over the back of his neck. “Oh, you know. Science is just… _Sans-sational._ ” God, W-D loved that one. Doc had a screeching creak of a laugh, textbook mad scientist, and Sans tried to wriggle one out of him every experiment and send all the interns scurrying under their desks.

Toriel giggled into her paw. “Do you happen to know any other experiments like this?”

“A couple.” That was nearly the end of his repertoire. He’d graduated from kiddie experiments to working the photon reader at Doc’s pretty early in his career. Familial nepotism and all that.

Toriel’s eyes gleamed in that familiar, terrifying way that meant she was going to ask him to do something that required effort. “Would you… oh, do you think… could you come demonstrate some of them for Frisk’s class? The children would love it, I am sure. Many of the others have been having the same troubles. It would help them so much! Maybe next Monday? You don’t have a shift then, do you?”

Nope, he thought, no way, just the thought of it was making him so bone-tired his eyelids were drooping, but what actually slipped through his teeth was, “Do you have any of those big plastic tub things? You know, like you could fill with water and float stuff in?”

“I believe there are some in the hall closet. Frisk, that was not two minutes of brushing,” she said as Frisk popped up around her knees. “Guess what? Your Uncle Sans is coming to school to do experiments with you and the other children!”

Frisk, a huge grin cracking their face, gave Sans a double thumbs-up. Well, no backing out now. He couldn’t disappoint the sum total of two of his favorite people at the same time.

“I, uh, gotta to work,” he said, ruffling the fur at the neck of his jacket, even though his night delivery shift at Grillby’s Two Surface Edition We Deliver Now didn’t start for another hour. He stooped to hug the kid and rose for a quick and messy nose-rub with Tori before hopping on his bike to drive in lazy circles around the neighborhood, his bones creaking in the cold, the stars Doc would have loved to chart blinking through stripes of hazy cloud.

* * *

 

Out on his delivery route he unzipped his hoodie and let the wind bleed into the space between his ribs, and thought of how W-D had always liked Queen Toriel. Or admired, more like. Thought it was a damn shame when she’d left the kingdom to founder with Fluffybuns in charge. The markets would never be the same without her deft hand to guide them. Or the monarchy’s substantial donations to the Royal Science Foundation.

He wondered what Doc would think of her now, so unlike the distant and regal profile stamped on Underground gold. Doc always did love himself some irony. “Hey, bro, yeah, I met the queen, turns out we’ve been friends for years, and she only lived a few feet away, only now she’s the ex-queen, and also I’m helping her raise her adopted human child on the surface—great kid, by the way, you’d like ‘em—and for reasons completely over my cranium she’s still wasting her time with me! What a riot, amirite?”

His shift didn’t end until late night, or early morning, he had never been able to tell an appreciable difference, but Paps was awake. Paps was most often awake, and very firm on the line between late night and early morning, and slinging something resembling food around on the stove.

“GOOD MORNING, BROTHER!” Paps announced. “I HAVE PRODUCED SUSTENANCE! ARE YOU HUNGRY? THAT IS A SILLY QUESTION. OF COURSE YOU ARE HUNGRY!”

“Actually, Grillbs gave me some grub before I came home.” Lies. Paps can tell, Sans knows by the way his grin droops, but he just grabs a bottle of ketchup from the fridge and sets it on the table. Paps would try to get him to push something down his gullet later in the day, but his brother really did have an excellent sense of timing. It was just one of the reasons why Paps was the coolest.

He tossed back half the bottle and rested his chin on his folded arms. “I, uh, got an extra job today. I’m gonna go do an experiment with Tori’s students on Monday.”

Paps twisted his head all the way around as he spooned his breakfast onto a plate. “AN EXPERIMENT? AN EXPERIMENT OF A SCIENTIFICAL NATURE?”

“Yeah. That.”

“BROTHER! THAT IS WONDERFUL NEWS! SO WONDERFUL I FEEL LIKE IT IS A GOOD TIME FOR INCIDENTAL MUSIC!”

His skull drooped over sideways as he shut his eyes. “Is it, though?”

“WELL. DON’T YOU MISS IT? DOING A SCIENCE? I WOULD MISS IT, IF IT WERE ME. OR, I SUPPOSE, IF I WERE YOU, AS I, THE GREAT PAPYRUS, HAVE NO SCIENTIFIC INCLINATIONS.”

He hadn’t done anything of a scientific inclination since coming to the surface, where there was so much work to do and jobs to work and also Frisk and Tori and hardly any time at all to take all of his government-mandated breaks. And even before that, it had been just that machine, over and over and over again, every day the machine, until all he saw when he was falling asleep (which was not very often, in those days) were curves and tangents swimming in a churning sea of flawed data points.

They’d called it the _Back to the Future_. W-D let him name that one too.

“Yeah. I guess you might say I’m like a charged skel-lepton without a partner, you know?”

Papyrus grimaced. “WHY MUST YOU PUN-ISH ME IN THIS WAY?” He paused to suck down an plateful of eggs, drumming his fingertips against the table. “SANS. DOES SHE KNOW?”

“Does she know what? That my favorite ketchup is Heinz? That I developed a secret, shameful shipping algorithm for Mettaton’s musical soap opera? That I can stack fifty hotdogs on my head?”

“SANS. STOP PLAGUING MY LIFE WITH ARTLESSLY DODGED QUESTIONS!”

He sighed, clasping his hands over the back of his neck. “Nope.”

“WELL.” Papyrus rolled his restless fingers into a fist. That was one thing he’d gotten from Doc—the hand thing. The two of them always twitching and tapping and waving and pointing. “THIS WILL STILL BE FUN, BROTHER! LET ME KNOW WHAT HELP YOU NEED! I AM SURE ALL THE CHILDREN WILL TAKE TO YOUR LAZY, LOVABLE CHARM AT ONCE!”

* * *

 

There were a lot of kids in Frisk’s class at the unfortunately named Monster School, Asgore’s final title bestowed as King.

Well, actually there were only about fifteen, but even two kids was one more kid than Sans was accustomed to handling. Fourteen monster kids and one human child all stared him down with fifteen-odd pairs (or in a couple cases, a triad, or just one) of beady little eyes as he stood behind the teacher’s desk holding a little tinfoil boat.

Why exactly was he doing this, again?

Reason number one sat up straighter in their seat, wiggling and wringing the hem of the sweater in excitement. They lifted a hand for a shy wave when he met their eyes.

Reason number two pushed her reading glasses up her nose, her pearly fangs gleaming as she offered an encouraging grin and flapped a hand his way. He’d never really seen Tori in the classroom before, scribbling on the chalkboard in her flower-patterned sundress. She looked good. Really good. And content, all the warm lines around her eyes crinkling as she surveyed her little kingdom of tiny monsters.

She could probably hold them back if they tried to eat him. Probably.

“Hey, squirts. I’m Sans, and this is Science Hour.” Did kids like dorky bone jokes? Frisk laughed at all his jokes, and Frisk was A Kid. “I’ll try to keep it light and _humerus_ for you guys.” That squeezed a few chuckles out of a few of them. Three out of fifteen could be worse. “Ready to test the waters with surface tension?”

Fifteen-odd groups of eyes blinked. Frisk waved again, a bit more bravely. He lifted his little aluminum foil boat and plopped it into his tub of water. “All right. What’s the worst vegetable to eat on a boat?” Frisk’s hand shot into the air. “That’s right. _Leeks_.”

To his surprise, only two of the water tubs tipped over as he demonstrated how to fold a boat, and only one kid accidentally sliced their thumb on a sharp edge of foil. Luckily Tori was there to press it between her paws and seal it up again.

Frisk made a truly excellent ship with a little foil sail and mast and skipped across the room to show him. Then they helped make another for their little pal, the scaly one without the arms, and the pair sat with their chins resting on their desks, watching the boats creep across the water, powered by a little dish soap in their wake.

“Yo, could you do this with a real boat, Mister Skeleton?” asked the little pal. M.K., Frisk had called them. “I’m asking for a friend.”

“Unfortunately not, short stuff. Unless you had a whole tank of dish soap and weren't in any hurry to get someplace. But I’ll tell you what you can do—can your friend fire magic bullets?”

“Of course I can!” M.K. insisted, puffing up their chest. “I mean, uh, yeah. They can.”

And Sans explained how if their hypothetical friend in their hypothetical boat fired bullets one way, the boat would go the other. “Yo, that’s really cool, Mr. Science Man!”

“Here, I’ll show you,” he said, and stuck one of his fingers in the tiny rowboat, wiggling it with an “Arrrgh!” M.K. giggled. “Just like this.”

A bunch of the squirts crowded around to watch him shoot off tiny bullets and zip the boat around the tank, and maybe sneak in some stuff about balancing forces and friction while he was at it. This might have not been the best idea, because afterward a few of them got in trouble for enacting a pirate fight between their two boats with magic bullet cannonfire. Turned out the classroom was almost as dangerous as a real lab.

“That went well, don’t you think?” said Tori as she mopped up a puddle decorated with glittering shards of tinfoil, undeterred by pint-sized warfare. “I think the children had a very nice time! One might say you really… floated their boats?” She laid a hand on Sans’s shoulder. “Thank you, Sans. It was very kind of you to come help.”

He shrugged. One time wasn’t really so bad. He might have even forgotten he wasn’t having fun there for a minute or two. “Eh, you know… it took a little pier pressure, but anything that gets my goat, y’know?”

She laughed her full, braying chuckle and brushed her nose against his cheekbone. “What are you doing later? Want to go out to Grillby’s? It’ll be my treat.”

“That’d be great,” he said over his shoulder. “And now I think I’m gonna go take a nap.”

“Oh, stop it with your pillow talk! There are children here,” said Toriel, and he chuckled into the hood of his jacket and stuck around to help her finish cleaning before he went home and collapsed in one of the hardest naps of his life.  Even counting back in his Master's.

* * *

 

It was another perfectly good date night when Frisk asked Sans to do science again. Well, the date part was over, but he’d shacked up with the kiddo at the table to help them with a puzzle while Tori whipped up a pie.

Frisk hesitated over their sketchpad as he took his turn before writing, _Everybody keeps asking me when my cool uncle is going to come back. We all had a lot of fun!_

“You did, huh? You know what else is fun? Letting your cool uncle finish his part in—“ He waggled a puzzle piece—“pieces.”

 _Oh_ , they signed, hunching their shoulders. _Okay_.

“Hey, squirt, I didn’t mean it like that. I’m sorry I made you frown. I had fun, too.” Not a lie, even though it was for Frisk’s benefit. Sure, it had been a little bit painful, like stepping on one of their Legos. But so had been the endless, bone-shearing late nights of working on the _Back to the Future_ , and he’d had fun with that too. The first time around, anyway.

“Tell you what. I’ll do another one.”

The things he did for that kid.

 _Really?_ asked Frisk, signing with such enthusiasm that the too-big sleeves of their sweater flopped over their hands.

“Really?” asked Toriel, clasping her hands over her chest. “You would? That is such a nice thing to offer, Sans. You’re really taking your generosity to… the maxilla.”

He couldn’t not laugh at that. The things he did for that woman.

She waited until he was done wheezing with laughter and cleared her throat. “Wait. I have another one. I looked this up on my internet phone earlier today. A photon checks into a hotel. The bellhop asks them if they have any baggage, and they say they don’t, because—“

“I’m traveling light,” he finished with her. Another Doc classic.

* * *

 

He’d exhausted all his kiddie experiments. Which meant it was time to call up the one person he knew who sometimes watched old elementary school science programs of her own free will.

He got Alphys’s phone message. “H-hello? You’ve reached Al—I mean, uh you’ve reached Upward Labs, and this is Dr. Alphys. I’ll call you back—ahem, please leave your name and number and I’ll call you back as soon as I can. Thanks!”

“Hey, Al. It’s Sans. I know you’re listening to the message right now to see what it’s about.” Not that he was guilty of the exact same thing on a regular basis. “I need a helping claw with something science-related. Call me back sometime.”

He’d seen Alphys around back in the day, of course, because there weren’t enough science students at Underground U that they couldn’t avoid making awkward eye contact in the hallways or sometimes sharing a study room. And W-D once hired her to do some software consulting for the Core and she kept lurking outside Sans’s cubicle trying to work up the courage to ask him if she could use the breakroom microwave to make some instant noodles.

But they had never been what either would call friends. And never in any other time, either, except for this one, and that was honestly more than a little strange. And more than a little of a waste.

He lounged around on the couch for the half hour it took for her to call him back. “H-hey, Sans! It’s Alphys! I mean, you knew that! What’s the thing? The thing you need help with?”

He explained. “Oh! Well! You asked the right lizard, I guess? I have, like, three terabytes worth of old edutainment shows. That I watch. Sometimes. I don’t know if that’s what you’re looking for?”

“That is exactly what I’m looking for.”

“Uh, great! I can just email them to you? Or, if you wanted, uh… my house is a wreck and I haven’t cleaned in forever but… you could come over and… watch… some? I’ll make instant noodles…”

She liked the shrimp flavor, he remembered. Not half bad if you drowned them in ketchup. “Yeah,” he said. “Let’s do it.”

* * *

 

Nineties kids’ science edutainment shows were a gold mine for stuff kids dug. Like the states of matter experiments, which were, as he promised Tori, “a real gas.” He was just starting to congratulate himself on a job nearly done when one of the little monsters with a big tuft of feathers tugged on the hem of his hoodie.

“Hey, Mister Skeleton, how do you know about all this stuff?”

“I’ve got a high school degree, kiddo.” Not a lie. He didn’t have to mention the three others. “Stay in school.”

“Have you ever worked in a lab, though? I always wanted to work in a secret lab.”

He imagined how well saying, “Sure, kid, I was squirreled up for years in a secret lab, working with my brother on a machine that would have changed time and saved the Underground, only the physics we slaved over was inherently flawed and it swallowed him instead to be forgotten forever!” would go over and instead threw a glance over his shoulder at Tori, who was stapling something up on the art wall. “Can’t say I have, kiddo. Sorry to disappoint.”

“But you knew that one Royal Scientist, right?” The kid’s eyes glimmered with excitement. Sans clenched his teeth and chanced another glance at Tori. She smiled brightly at him, mouthing “Nice work, funnybones!”

The kid blinked, frowning. “You know, the Royal Scientist, Dr. Alphys! She’s really cool, right?”

His shoulders sagged down from around his ears. “Oh, yeah, Alphys. She’s plenty cool. She gave me some ideas for this lesson. But now… it’s time for some math.” He waved off a smatter of protests. “Kiddos, math and science go together like hot dogs and ketchup. It looks scary, I promise. Like me!” He winked. “But really math is just a big old softie, just like yours truly.” And W-D, the terror of lab techs everywhere with his long, spindly shadow and restless hands. And that laugh.

The children, pouting, hunkered down to work, and he still managed to stick his ending joke, “Remember, squirts… you all matter!” That actually roused a few belly laughs. Either his material was improving or he was doing an excellent job of corrupting these youths. Or, rather, expanding their pun-tential.

Tori bent to hug him, and whispered in his ear, “Next week?”

Already this far in it now. What could it hurt, really? “Sure, yeah.”

* * *

 

Next week, after showing the class the wonders of bending light, he ate his cafeteria-regulation hotdog slathered in ketchup at one of the picnic tables outside, watching some of the sprouts run laps around the soccer field at Coach Undyne’s direction. The sun was prickling the back of his skull and the freshly cut grass scratched his ankles. Doc had been allergic to grass, and couldn’t stand bright lights of any kind, which was why the lab was kept in a half-lit gloomy murk like some kind of videogame mad scientist nightmare.

He wished Doc could’ve seen the sun once. He wished he could’ve heard Doc grumble under his breath about the sun just once.

Frisk was obviously a good deal faster than their brethren, but after a round of showing off they slowed down to jog with a couple of their half-pint friends. A few of them waved at him on their way around. He was getting downright famous.

Undyne’s whistle blasted ten inches from his cranium. “Hey, nerd!” she said, plopping down beside him and nearly uprooting the table. He bounced and lunged to save his lunch. “Heard you were giving Tori a helping hand! That’s real stand-up of you, you know? Because let’s face it.” She spared a quick glance around the periphery for any hide or hair of Toriel. “Right now this school kinda sucks.”

“Coach Undyne said sucks!” squealed one of the half-pints.

Undyne shook her fist at the gaggle of loitering children. “You champs better pick up the pace, or you’ll have to do push-ups!”

“I don’t have arms!” replied the child with glee as they flapped their fluffy wings.

Undyne turned back to Sans with a snort. “I mean, like, everything kinda sucks when it’s first getting started, right? Believe me, Alphys has shown me a ton of documentaries, and we have a long way to go before we’re up to snuff.” She sucked in a huge breath, her nostrils flaring, and launched into a tirade about fighting dragons and giant robots and transformation sequences and student councils with way too much centralized power. Sans dozed off a couple times.

But she finished with, “And Alphys says the science department is pretty balls. But she’s scared of crowds, especially crowds of kids, so she hasn’t done anything about it.”

Her declaration was followed by a chorus of snickers and the word “Balls!” chanted in whispers. “You heard me, small champs! Keep at it!”

“But we did five laps, Coach Undyne!” called a short, blob-shaped one in a pink striped sweater. “Now you gotta bench press us!”

The rest of the short stacks took up the cry of “Bench press, bench press!” and Undyne rose from the table with a sigh.

“All right. Line up seven at a time.” She slugged Sans in the shoulder, popping his joint. “See you later, nerd! Say hi to Paps for me!”

As Undyne, her considerable triceps fluttering, grunted and heaved a stack of children into the air, Frisk drifted on over with another fourth-grader in tow, a little raccoon-type with thick, heavy-rimmed glasses. The other kid was twiddling with one of their thumbs. Frisk patted them on the shoulder and nudged them forward again when they didn't stop fiddling.

“Excuse me, Mister Science Skeleton.” They focused intently at their toes. “Umm… Frisk was telling me that sometimes you help them with their homework, and um… I have trouble sometimes and... would you help me too? Like, be my tutor or something?” Frisk nudged once more. “Please?”

Sans narrowed his eyes at Frisk, who shrugged with a grin. _Tally doesn’t have anybody at home to help her_ , they signed. _Come on, Uncle Sans! You know you want to_! They pulled an exaggerated pout. _P-L-E-A-S-E_!

To his surprise, he thought of Frisk’s glowing smile when they managed to get a problem just right, and the way their cheeks scrunched up when they played with the density jar, and found he actually did kind of want to. He wondered if this was what W-D felt like, leaning down with him in the grass, kneeling in cramped cubicles night after night, phalanges tracing down lines and lines and lines of equations.

“Well. I gotta ask Tori—I mean, uh, Ms. Toriel first. But I'm sure we can set something up, okay? Don't let that frown get you upside down, okay, Tally?” The kid wobbled their chin and let Frisk lead them back towards Undyne, who hoisted them both up on her shoulders with a grin.

* * *

 

Later that night he asked Tori if she wanted help grading that week’s homework. “I have no idea why you’d wish to,” she said with a tired smile, rubbing her hand over her forehead, “but of course I would welcome the help.”

After a silent fifteen minutes of marking and circling and noting _Nice try, bucko, points for style_ for a child who’d “found” x by circling it in the problem stem, he tapped his pen against the edge of the table and asked Tori about tutoring. “One of the kids brought it up today, and I think it might not totally be an awful idea, y’know? And maybe I could help you with grading stuff sometimes, and the curriculum.  Do some stuff with the other classes. You know.”

Tori’s brow furrowed and she glanced at him sideways through eyes puffy with exhaustion. “Sans, dear, you know I think that is very kind of you.” Not an auspicious start. “I don’t see why you can’t use one of the spare rooms for some tutoring, sometimes, but… are you certain you’re up for that much? After all, you’ve never done anything like this before.”

She turned her narrow-eyed gaze on him. “Have you?”

He gulped and drummed his fingers against the edge of the table. Just like Doc and Paps. “Nah.” He shrugged. “What you see is what you get.”

The low road of denial and cowardice. As if he’d ever expected anything else of himself.

Tori closed her eyes and leaned back in her chair. “Well,” she said, and fumbled about on the table until her paw closed over his hand. “I like what I see. Very much.”

His fingers twitched and bent around hers. Doc would’ve liked Toriel a lot, he’s sure. The real Toriel, the woman who joked behind doors and baked a mean pie and loved any child she found like they’d always, always been hers. The real Toriel who loved him, somehow, even though that confused him only every single day.

“I gotta go grab something,” he said. “From my place. I’ll be back in fifteen.”

* * *

 

When he returned from rifling through his stacks of photos and charts and all the flawed, doomed math of the time machine, he found Frisk in the front yard, bundled up in their puffy jacket. They clutched a paper sled kite, chewing their bottom lip as they wrote a message for him on its back. _I can’t get the tail right. Can you give me some wind? Please?_

As Frisk let the little scrap of paper and dowel loose into the air, Sans summoned a row of bones like a fan and let loose. The little kite drifted low, made a tight turn, and promptly dipped back down onto the grass. Frisk knelt to collect its remains.

 _The third one was way better,_ they signed, and went to make a mark in their little notebook.

Frisk was doing _experiments_. They were even making some rudimentary wind force calculations in the margins. His ribs swelled with pride.

He fiddled with the crumpled lump of paper in his jacket pocket as they adjusted dowels and strings and threw another kite into the air, pale and bright as the missing moon in the empty, starless sky. He tilted his head back to watch the velvety clouds, and didn’t realize Frisk was waiting for his next move until they waved their hands in front of his face.

“Whoa. Sorry, kid. Just thinkin.’”

Frisk settled down next to him with their kite in their lap. _Whatcha thinkin’ about?_

“I’ve gotta talk to your mom about something.”

_Really? Like what?_

“You know. Stuff.” He yanked the drawing from his pocket and held it out to show them.  A drawing of three figures and the words  _Never forget_ , handled so often it was soft as cloth, and faded at the folds. “This kinda stuff.”

Frisk wrinkled their nose. _What is it?_

“It’s a crappy drawing, Frisk.”

Frisk brightened and bent over their kite. _Are you gonna talk to her about, stuff-stuff? Like, that machine in your lab stuff? That old picture stuff? That stuff?_

“Never get anything past you, huh?” There would never be any secrets from that kid. Frisk always uncovered hidden chocolate, secret birthday party plans, and his struggles with his non-existent past. They could make a damn good scientist someday, with that kind of curiosity.

 _She’ll be really glad!_ They clapped their hands together. _Mom kind of wishes you’d talk to her about stuff more. You know how she is._

He did know how she was. He knew this her, the one that was big and soft and solid and real, who would listen and laugh in all the right places whether she believed him or not. “So I’d appreciate if you stayed out here for awhile.”

 _Sure. I’ll be here with my kites. I’ll make you a really good one!_ And they set another free as he elbowed through the door to where Tori was settling her pie on top of the stove to cool.

He placed his crumpled drawing on the table and yanked up a chair. “Tori,” he said, “If anything, I am probably overqualified to teach fourth graders how to multiply. What do you call a skeleton with a Ph.D.?”

“What?” she asked as she sat beside him, placing steaming mugs in front of them. Hers held tea, his hot ketchup. The good stuff. 

“Someone with two thousand gold in student _bones_! Also, myself. Because I have a doctorate in theoretical physics.”

She let out a sharp, surprised chuckle. “Just how much of that… was a joke?”

“Only the first half. The rest of it…“ He pointed at his grinning mouth. “It’s the absolute _tooth._ ”

She twisted her hands around her mug, considering.

“I worked in the Royal Labs for awhile, back in the day. On the Core. And on some other stuff that we hoped might change things for the Underground.” Let no one ever say Doc hadn't thought big. “And… stuff went not so great. Really not so great. As you can guess. Since I ended up a sentry out in Snowdin Woods. And I never said anything to you about it.” There was a dragging, curious weight in his sternum, and he felt cheated. Wasn’t letting stuff off your chest supposed to make you feel lighter?

“I had guessed… well, I had not really guessed. But I had expected something… of that nature. Thank you, Sans,” she said finally. “For telling me, and trusting me.”

“Don’t thank me yet.” He slapped the drawing. “I’m not done. I still gotta tell you about my brother.”

Tori squinted down at his poorly-drawn handiwork. “Which one is supposed to be Papyrus?”

Everybody was a critic. He was a damn theoretical physicist, not an artist.

He pointed to the tall squiggle. “Yeah. That one’s Paps. The chubby one is yours truly. And this guy—“ he gestured to the skinny figure with outspread hands being swallowed by a big white rectangle of a lab coat. “Is our other brother. Royal Scientist, unfortunately creepy laugh, big hand-talker? You know him. Or, uh, you did know him. Once.”

Tori blinked in confusion. “I don’t believe I do. You must be confused. We had no scientist before Dr. Alphys.”

“I’m confused, all right, but you definitely did. It’s… it’s kind of a long story. But it’s got great special effects and some some bad laughs. I do all the stunts myself. Three out of five stars on Undernet Reviews.”

She scooted her chair closer and placed her arm over his shoulders. “I’m on familiar terms with long stories, myself,” she said. That was the understatement of the year.

He leaned against her with a sigh. “All right. It’s time to repent… for my _sines_.” She laughed gently and drew him closer.

“It starts like this.”

**Author's Note:**

> To my pleasant surprise, the Bill Nye the Science Guy website is still up and running and provided free kiddie experiments for me to steal.
> 
> I'm a personal fan of Big Bro Gaster, but Dadster is also quality. Heck, all Gasters are quality. Carry on with your bad selves, Gaster folk.
> 
> Also, I know the Sans drinking nothing but ketchup meme is overblown but... was that ever gonna stop me? NAH.
> 
> As always, thanks for reading!


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